Field of the Invention
The inventions disclosed and taught herein relate generally to polyurethanes and their manufacture, and more specifically, are related to methods for the manufacture of polyurethane foams of a variety of densities and which use sugars, carbohydrates or natural polyols as the primary source of the polyol component, and utilizes deep eutectic solvents and/or ionic liquids as a solvent for the polyol system.
Description of the Related Art
Polyurethane foams articles are used extensively in a wide array of commercial and industrial applications. The popularity of polyurethane foam articles is due in part to the fact that the physical properties of a polyurethane foam article may be selectively altered based on the formulation of reactants which form the polyurethane foam article. The formulation may be developed to provide a polyurethane foam article that is soft, flexible and open-celled which can be used in applications such as seat cushions. On the other hand, the formulation may be developed to provide a polyurethane foam article that is rigid, structural, thermally resistant and closed-celled and which therefore can be used as a thermal insulation panel.
The most common method of forming polyurethane foam articles is the mixing and, subsequent reaction, of a polyol (e.g. a resin composition) with an isocyanate in the presence of a blowing agent. Generally, when the resin composition is mixed with the isocyanate to form a reaction mixture in the presence of the blowing agent, a urethane polymerization reaction occurs. As the urethane polymerization reaction occurs, the reaction mixture cross-links to form the polyurethane and gas is simultaneously formed and released. Through the process of nucleation, the gas foams the reaction mixture thereby forming voids or cells in the polyurethane foam article.
The resin composition typically comprises one or more polyols, a cell regulating agent, catalysts, and various other additives. The blowing agent creates the cells in the polyurethane foam article as described above. The catalyst controls reaction kinetics to improve the timing of the polymerization reaction by balancing a gel reaction and the blowing agent to create the polyurethane foam article, which is stable. Other additives, such as adhesion promoting agents, may be added to the formulation in order to facilitate wet out of the reaction mixture and promotes adhesion of the polyurethane foam article to substrates upon which the polyurethane foam article is disposed. For example, the substrate may be a thermoplastic shell or thermoplastic liner of a picnic cooler. The density and rigidity of the polyurethane foam article may be controlled by varying the chemistry of the isocyanate, the resin composition and/or the blowing agent, and amounts thereof. Other additives that are often included within the polyurethane foam product are fire retardants, typically halogenated—(e.g., brominated and chlorinated materials) and phosphorus-containing retardant materials.
Plastic foams have been utilized as thermal insulating materials, light weight construction materials, and flotation materials and for a wide variety of other uses because of their excellent properties. Until recently, their use has been somewhat limited in environments where there is danger of fire because of their substantial fuel contribution, their contribution to rapid flame spread and the fact that they generate large quantities of noxious smoke on thermal decomposition when burned or heated to an elevated temperature. This has limited the commercial development of plastic foams, and large amounts of money and much research time have been expended in attempts to alleviate these problems.
With the present interest in conserving heating fuel, many existing buildings are installing additional insulation, and newly constructed buildings are including more insulation than was formerly used.
A previously common type of foam insulation for existing structures are urea formaldehyde foams, which are foamed in place between the outside wall and the inside wall of the structure, with or without additional, fiberglass insulation. Fiberglass insulation alone can be considered to be porous in nature since it is generally a mat of fine glass fibers, which can contribute to lower insulation values by allowing air circulation within the walls. Foam insulations, however, form an air barrier between the interior and exterior walls of a structure, and thus form a generally impervious barrier to air circulation, thereby making them better insulation materials. Unfortunately, the urea formaldehyde foam that has been used spontaneously decomposes, releasing formaldehyde fumes in quantities which may be toxic. The use of urea formaldehyde foams in construction is prohibited in many building codes for this reason.
Another type of material often used for insulation is polyurethane foam. However, polyurethane foam provides a substantial fuel contribution, spreads flame rapidly, and releases toxic gases including carbon dioxide, carbon monoxide and hydrogen cyanide when burned. Additionally, conventional polyurethane foam articles are made from petroleum-based polyol. As a non-renewable feedstock, petroleum has both environmental and financial drawbacks. Accordingly, there are environmental, economic, and commercial advantages associated with the use of polyols based on renewable feedstocks such as natural oils to make what some term “bio-based” polyurethane foam articles.
Rigid polyurethane foams are generally prepared by reacting an organic polyisocyanate with a polyol. For most commercial purposes, the reaction is conducted in the presence of a foaming agent, surfactant, catalyst and possibly other ingredients. In order to reduce the cost of preparing these foams, efforts have been made to employ polysaccharides such as starch or cellulose as a polyol reactant in their preparation. The use of such alternative polyol materials has been unsatisfactory to date because of the poor physical properties of the foams produced. For example, oxyalkylated starch yields satisfactory foams, but the direct oxyalkylation of starch results in uncontrolled degradation or decomposition of the starch. When such products are used in the production of foams, the foams do not have uniform chemical or physical properties.
In addition to the above, developing new green solvents is a key subject in Green Chemistry. As a result, a great deal of attention has been given to developing Ionic liquids (ILs) and deep eutectic solvents as a replacement for conventional organic solvents systems, as conventional solvent system tend to be harsh on the environment. Recently it has been discovered that many plant abundant primary metabolites change their state from solid to liquid when they are mixed in proper ratio [1]. This finding made us hypothesize that deep eutectic solvent systems or ionic liquids can replace either aqueous or conventional organic solvent systems in the production of Isocyanate-based polyurethanes.
It is an understood phenomenon that pure solid chemicals can become liquid by mixing in certain ratios as in the case of ionic liquids and deep eutectic solvents. For example, when prilled urea (135° C. melting point) and choline chloride (302° C. melting point) are mixed together in approximately a 1 to 1 mass ratio, together they form a liquid that has a freezing point of approximately 12° C. Another example is the mixture of ammonium thiocyanate (150° C. melting point) with urea in roughly a 1.5 to 1 mass ratio that results in forming a liquid having a melting point around 25° C.
Therefore, in general, Ionic liquids (ILs) are a class of organic salts with a low melting point. Recently, with the aim of developing environmentally friendly solvents, ILs have received increasing attention because they have a negligible vapor pressure and can be tailored concerning polarity and selectivity for different applications such as solvents used for metal cleaning prior to electroplating. Or, because these solvents are conductive they have a potential application in electropolishing. Compared to ordinary solvents, eutectic solvents also have a very low VOC and are non-flammable.
Another type of solvent with similar physical properties and phase behavior to ILs are deep eutectic solvents (DES) [S. Z. E. Abedin, F. Endres, Acc. Chem. Res., Vol. 40, pp. 1106-1113 (2007)]. These solvents are mixtures of compounds that have a much lower melting point than that of any of its individual components, mainly due to the generation of intermolecular hydrogen bonds. The principle of creating ILs and DES was demonstrated for mixtures of quaternary ammonium salts [4] with a range of amides and carboxylic acids [5], and later extended to choline chloride with alcohols [6], and urea with sugars or organic acids [7,8]. Some features of these DES make that they have an advantage over ILs because they are easier to prepare with high purity at low cost. Higher melting points of many DES, however, can hamper their application as a green solvent at room temperature. Compared to the broad applications of ILs [9-12], the application of DES has been so far limited to organic reactions [7,8,13], organic extractions [14], electrochemistry [15-17], and enzyme reactions carried out at 60° C. [6]. Moreover, the synthetic ILs suffer from high toxicity of some of the ingredients [18,19], which is hampering their use in pharmaceutical and food related products.
We have demonstrated herein that new technology development of polyurethane foams, is benefited by the application of ionic liquids and or deep eutectic solvent systems in developing polyol formulations. The benefit of using non-aqueous polar solvent systems such as IL's and DES with, in particular sugar based polyol systems, is that the water used to dissolve the polyols, such as glucose, sucrose, fructose and the like, is highly reduced or eliminated altogether. This allows for a much higher urethane index, higher urethane densities, stronger, more rigid, and dimensionally stable materials when used to make polyurethanes. Therefore, the application range of “green” bio-based polyurethanes are extended beyond the current applications to date.
The inventions disclosed and taught herein are directed to polyurethane foams using natural or plant-based polyols, such as sucrose, for the polyol component in the foam composition, and ionic liquids (ILs) and/or deep eutectic solvents (DES) to dissolve the natural polyols, wherein the dissolved polyols are then used to manufacture polyurethane foams with specific densities. The resultant foams also is exhibit a high degree of burn resistance.